(i) Field of the Invention
This invention relates to the rejuvenation of aged asphaltic pavement.
(ii) Description of the Prior Art
As asphaltic concrete pavement ages, the asphalt cement becomes harder. This leads to the deterioration of the pavement. During this age hardening the heavy asphaltic component contents increase. A rejuvenation agent for such aged asphaltic concrete must be of sufficiently low viscosity to lower the viscosity of the aged asphalt to desired levels. It also must have a high polar to non-polar component ratio to assure compatibility with the high heavy asphaltic content in the asphalt of the salvaged aged asphaltic pavement.
Recycling of salvaged asphalt pavement has significant economic advantages because significant amounts of virgin asphalt and aggregates are needed to produce a new asphaltic cement pavement. Further, salvaged asphalt pavement contains high quality aggregates which may be either disposed of in dump sites or may be used in low performance applications. The current situation in North America concerning the hot recycle of salvaged asphalt pavement is quite extensively described in a paper by W. D. Robertson et al entitled "Mix Design--The Key to Successful Pavement Recycling" and published in the Canadian Technical Asphalt Association Proceedings of 1988, p. 330. The contents of such paper are herein incorporated by reference.
One common practice at this time is to mix old milled asphalt pavement material with soft virgin asphalt and then to heat the whole mixture by the addition of preheated virgin aggregate. The current limit in Ontario, Canada of old pavement utilization is 50%, due to environmental regulations for the amount of smoke produced when the hot aggregate is added.
Specifications for recycling agents used in hot-mix recycling are described in a paper by Kari et al in "Asphalt Paving Technology" of 1980 p. 177. The contents of such paper are herein incorporated by reference.
Cold in place recycling of asphalt pavements is increasing in popularity, as described by Wood et al in "Transportation Research Record" #1178 of 1988. The contents of such paper are herein incorporated by reference.
N. Paul Khosla described the use of emulsified recycling agents in "Asphalt Paving Technology" of 982 p. 522. The contents of such paper are herein incorporated by reference.
However, other approaches to recycling are possible. These include methods that require minimal or no heating. Several approaches are described in the following patents:
U.S. Pat. No. 4,373,961, patented Feb.15, 1983 by E. M. Stone, provided a process and composition for recycling old asphalt pavements into new pavements. It was accomplished by adding a special asphalt emulsion to the crushed old asphaltic pavement material without requiring the addition of new aggregate or heating. The old material was then cemented at the ambient temperature into a new durable composition of high stability and water resistant, softening or other appreciable change in the old asphalt, by selection of the degree of hardness and character of the asphalt base stock in the special emulsion. Thus the patentee provided a process for recycling old asphalt pavements into new pavements comprising the steps of crushing the old asphalt pavement to form an aggregate comprising asphalt and mineral matter and then emulsifying an asphalt base stock with water to form an emulsion. The aggregate was then mixed with the emulsion to form a pavement material. The pavement material was then laid and compacted as a pavement course.
Other procedures in the prior art attempted to solve the problem by improving the asphalt compositions. Thus, U.S. Pat. No. 2,904,494, patented Sep. 15, 1959 by R. L. Griffin, provided an improvement in the process of preparing asphalts having improved aging stability. The patented steps included distilling a petroleum residue to provide a reduced residue having improved stability. That residue was then blended with an asphaltic oil.
Other patents have attempted to solve the problem by adding various agents to asphalt paving compositions. Thus, U.S. Pat. No. 3,793,189, patented Feb. 19, 1974 by L. W. Corbett, provided asphaltic compositions suitable for use in paving formulations and having desirable viscosity, temperature susceptibility and ductility properties by combining propane-precipitated asphalt, asphaltenes and a liquid petroleum derivative, e.g., a heavy distillate or residual oil.
Other patents were directed to reconditioning bituminous pavements. Thus, U.S. Pat. No. 3,221,615, patented Dec. 7, 1965 by E. W. McGovern, provided for the revitalization of bituminous pavements which were in the process of becoming or which have become dry and brittle through aging and weathering by applying thereto a composition which was derived from coal tar and comprised a mixture of di-, tri- and tetracyclic aromatic compounds and their alkyl homologs containing lower alkyl groups together with a significant amount of phenolic and hydroxy derivatives.
U.S. Pat. No. 4,278,469, patented Jul. 14, 1981, by T. Y. Yan et al, provided a ductile asphaltic composition adapted for repairing and surfacing distressed asphalt pavements which comprised a blend of an asphalt component selected from marginal asphalt materials, a highly aromatic petroleum refinery residuum solvent component, and a polymeric component which is substantially asphalt-soluble.
U.S. Pat. No. 4,279,660, patented Jul. 21, 1981, by I. Kamo et al, provided a process for the recovery and reutilization of materials in existing asphalt pavements, comprising comminuting existing asphalt pavement, subjecting the comminuted pieces to the action of a solvent in a dissolving zone to separate asphalt from other component materials, recovering solvent and asphalt dissolved therein from the zone separately from the other materials, drying and classifying the other material according to size, separating asphalt from the solvent, and transferring separated asphalt and the size-classified other materials to storage zones for subsequent reuse in the preparation of asphalt pavement.
U.S. Pat. No. 4,325,738, patented Apr. 20, 1982, by H. Plancher, provided a technique for substantially improving the useful life of asphalts by adding a minor amount of a moisture-damage-inhibiting agent selected from compounds having a pyridine moiety, including acid salts of such compounds. A shale oil fraction was said to serve as the source of the improving agent and may simply be blended with conventional petroleum asphalts.
U.S. Pat. No. 4,549,834, patented Oct. 29, 1985, by J. P. Allen, provided an asphaltic composition especially suitable for rejuvenating recycled asphalt-aggregate road compositions, consisting essentially of asphaltic oils, asphaltic resins, and asphaltic pitch.